Developers of 3G wireless communication systems are considering LTE of the 3G systems to develop a new radio access network for providing a high-data-rate, low-latency, packet-optimized, improved system with higher capacity and better coverage. In order to achieve these goals, instead of using code division multiple access (CDMA) which is currently used in 3G systems, orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) are proposed as air interfaces of LTE of 3G to be used in downlink and uplink transmissions, respectively. In parallel, also being considered is an evolved packet-optimized system, so called HSPA+, which is a conventional CDMA-based system.
The basic uplink transmission scheme in LTE is based on a low peak-to-average power ratio (PAPR) single-carrier FDMA transmission with a cyclic prefix to achieve uplink inter-user orthogonality and to enable efficient frequency-domain equalization at the receiver side. Both localized and distributed transmission may be used to support both frequency-adaptive and frequency-diversity transmission. The uplink transmission scheme in HSPA+ is based on CDMA.
FIG. 1 shows a basic sub-frame structure for uplink transmission proposed in LTE. The sub-frame includes six long blocks (LBs) and two short blocks (SBs). Alternatively, three SBs may be used per sub-frame. FIG. 2 shows the allocation of subcarrier blocks in the frequency domain. Seven (7) orthogonal frequency division multiplexing (OFDM) symbols are transmitted during a 0.5 msec subframe over allocated subcarriers, (e.g., ten (10) subcarriers). In-band pilot symbols and data symbols are multiplexed in the subcarriers as shown in FIG. 2.
Due to the change of the physical layer structure, new attributes and resource allocation scheme for uplink transmission, TFC selection procedures defined in the current wireless communication standards cannot deal with the new system requirement and thus part of it should be re-designed. In LTE, the number of subcarrier blocks and the number of TTIs are new radio resources to be considered for TFC selection, and the radio resource and parameters reallocated for the retransmission of the same data block may be different from what are used for the initial transmission. In HSPA+ and LTE, even when the radio resources and parameters allocated for the retransmission of the same data block remain the same as what are used for the initial transmission, using the same TFC selection, (especially the same modulation and coding scheme (MCS)), may not be efficient to overcome the fading channel and to reduce the number of retransmissions.
Therefore, it would be desirable to provide a new TFC selection procedure for one set of data blocks among a plurality of sets of data blocks to take into account these new features and to change the MCS for the subsequent retransmissions to adapt to the channel conditions.